Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

265
FXUS63 KLOT 161823 CCA
AFDLOT

Area Forecast Discussion...CORRECTED
National Weather Service Chicago/Romeoville, IL
123 PM CDT Sat May 16 2026

.KEY MESSAGES...

- Uncertain storm chances this afternoon, with many areas
  potentially/probably staying dry, then a better chance for
  showers and storms this evening-early Sunday, especially with
  westward extent.

- Expect more widespread showers and at least scattered storms
  at times Monday-Tuesday, some of which may be severe.

- Summer-like warmth and humidity is in store this weekend
  through early next workweek. Cooler conditions then return
  midweek.

&&

.UPDATE...
Issued at 1227 PM CDT Sat May 16 2026

We`ve been monitoring the northward progress of outflow
boundaries and/or gravity waves emanating from convection over
west central/southwest IL. There`s a play for modest low-level
forcing from the northward lifting boundaries to initiate widely
scattered storms near and especially north of I-80 this
afternoon-early evening across primarily interior sections of IL.
However, the subsident regime in the wake of this morning`s
convectively modulated short-wave could serve to be a limiting
factor. The biggest wildcard is dew point trends with respect to
stronger destabilization. More aggressive CAM solutions
convective coverage wise depict a notable uptick in Tds
coincident with the arrival of the outflow boundaries.

To this point, these solutions have been verifying higher than
observed dew points, so it`s possible this will continue to be
the case. Opted to account for the lower end potential for CI
across interior northern IL this afternoon with PoPs into the
20-30% range. While it`s certainly plausible a lion`s share of
the area remains dry through the rest of the daylight hours, if
any storms do occur, there`s enough mid-level flow paired with
steep mid-level lapse rates for modest storm organization and a
corresponding localized damaging downburst wind threat (and
perhaps isolated large hail).

There does appear to be a better chance for increased shower and
thunderstorm coverage later this evening and overnight,
especially over the western half or third of the CWA. Will
address this in the full afternoon forecast discussion.

Castro

&&

.DISCUSSION...
Issued at 240 AM CDT Sat May 16 2026

Early this morning:

The last of the initial band of showers that moved across
southern Wisconsin and far northern Illinois earlier this
morning is moving out over Lake Michigan. The trailing outflow
boundary and residual cold pool extending southwest of these
storms have put a damper on additional shower and storm
coverage. The leading edge of this outflow could lead to
additional isolated shower development but has been unsuccessful
thus far. Meanwhile, a secondary line of showers and storms in
central Iowa continues to progress east toward the region which
may still give the rest of an area a chance to see a period of
showers and isolated (non-severe) storms toward the pre-dawn
hours through mid-morning, ending from northwest to southeast.

Today and tonight:

A remnant outflow boundary/gravity wave from the early AM
storms is expected to stall out over central IL/IN later this
morning where an east to west oriented axis of showers and
embedded storms may attempt to redevelop during the day along
this feature. There remains some uncertainty in where exactly
it stalls, so have maintained 20-30% shower/storm chances south
of a Pontiac to Rensselaer line in case it ends up farther
north. It could very well remain just outside of the local area
though.

As we head into the rest of the day temperatures are expected
to warm into the lower-to-mid 80s (locally cooler near/under any
showers to the south). In tandem, the airmass will become
increasingly unstable with little to no capping in place.
However, the majority of the area is mostly removed from any
notable forcing mechanisms other than a potential weak lake
breeze in the afternoon. As a result, hi-res guidance remains
highly variable from run to run in the the placement and
coverage of potential for spotty thunderstorms during the
day. Accordingly, capped shower/storm chances at 15-20% for the
to lower confidence. The more likely scenario is that the
majority of the area remains dry the rest of the daytime hours.

A mid-level disturbance lifts into the area late this evening
and overnight which could bring renewed shower and storm
chances to portions of the area, highest near and north of I-80
(40%). We will also have to keep an eye on upstream convective
trends in the event that a more vigorous convective complex
happens to hold together across Iowa. Stay tuned.

Petr


Sunday onward:

Guidance continues to indicate breezy (30-35 mph gusts) south
winds will develop Sunday afternoon, after the warm front lifts
north of the area. With any morning showers/storms (favoring
near/north of I-88) departing and decreasing cloud cover in the
warm sector, high temperatures in the mid-upper 80s appear
likely at this distance. The exception may be near the Lake
County IL shore, as a just east of south component to the winds
could cap highs in the 70s later in the day. Breezy and mild
conditions look to persist Sunday night, with lows generally in
the mid to upper 60s.

Thunderstorm chances then return Monday and Tuesday, as a
Central Plains surface low pressure slowly lifts northeast
through the northern Great Lakes and eventually trails a cold
front through the forecast area. Ahead of the cold front, the
forecast area will reside in breezy warm southerly flow,
characterized by daytime temperatures in the 80s and increasing
low-level moisture return (surface dew points potentially upper
60s-to near 70F) from the western Gulf. Resulting instability,
combined with mid-level flow near 40 kts would potentially
support strong/severe thunderstorms (as well as some threat for
flooding given high column moisture), though forcing mechanisms
remain unclear within the broad warm sector making convective
timing/evolution of low confidence at this distance. Monday`s
overall messy look also lends uncertainty to how much
instability can be realized at peak heating, particularly if
morning activity ends up fairly widespread.

On Tuesday, in the wake of probable continued overnight/early
day convection, the aforementioned cold front will approach.
It`s not uncommon in these setups for renewed storms and any
associated strong to severe threat ahead of the front to focus
primarily near/southeast of I-55, though time will tell in this
regard. For the Monday-Tuesday period, SPC continues to extend
severe probabilities into our area, which appear reasonable.
Quiet and cooler conditions are then expected by mid-week, as
surface high pressure builds across the region in the wake of
the Tuesday cold frontal passage.

Castro/Ratzer

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1207 PM CDT Sat May 16 2026

Southwesterly winds, with some intermittent 15-20 kt gusts, will
continue this afternoon.

An outflow boundary continues to lift northward out of central
Illinois where convection has been fairly widespread this
morning. On its current trajectory, this feature may be nearing
the southern c90 TRACON towards 20z, and then may continue
lifting north through the rest of the afternoon. It remains
unclear if additional showers and thunderstorms will re-develop
on this boundary, or out of currently-developing cumulus
straddling the I-88 corridor, given the presence of modest
subsidence in the wake of this morning`s activity and a lack of
more substantive large scale forcing in the region. Given a
warm, moist, and unstable airmass in place this afternoon, a
potential for isolated to scattered thunderstorms exists, but
chances/confidence still are too low to hop on VCTS or TEMPO TSRA
mentions in the TAFs.

This evening, winds will trend southeasterly. Additional showers
and thunderstorms may push out of eastern Iowa overnight into
early Sunday morning. The greatest chances currently exists near
RFD.

Thereafter, wind trends into Sunday afternoon remain a bit
unclear at the Chicago-area terminals. Initially southeasterly
winds will likely become SSW and gusty, especially at MDW, and
GYY, but there is some potential that a lake breeze remains in
place INVOF ORD. At this time, will show the development of SSW
winds at ORD during the afternoon, but note that these wind
trends remain a bit uncertain at this range.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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